A data backup appliance combines software and hardware in a single box, configured and ready to go. Once considered just an SMB option, these products are ready for the enterprise.

Backup appliances were originally designed for small companies or departmental backup environments. They provided an all-in-one backup solution that was easy to install and run, but they didn't offer the features, functionality or scalability required for midsize or larger environments. But with improvements to both hardware and software, data backup appliances have become viable solutions for companies of almost any size, even some in the enterprise space.

Data backup appliance defined

For our discussion, we'll define a data backup appliance as a complete backup system that includes hardware to store backed up data and software that controls the process of copying data from client servers and computers to the storage system. Many of these products can write data to direct-attached storage (DAS) or networked storage (NAS or SAN), but we won't consider that a requirement.

That definition is in contrast to another familiar term, purpose-built backup appliance (PBBA), which has been used to describe dedicated backup storage systems that are typically used as targets for backup software but don't always include that software. Virtual backup appliances -- backup applications that run in a virtual machine -- also aren't included in our definition, although many of the data backup appliance vendors offer that option as well.

Backup appliances were used as alternatives to traditional backup infrastructures, which typically included a separate software app and storage devices, originally tape drives but more recently disk arrays. Backup appliances were primarily intended for smaller firms that didn't have the IT resources to design, implement and operate traditional backup systems, which could get rather complex.

Early backup appliances were better suited for small to midsize companies due to their somewhat limited scalability, both in capacity and performance, and they often lacked the more sophisticated features that traditional backup applications include.

More recently, with improvements in storage and processing technologies (and the continuing decline in storage costs), data backup appliances have evolved into devices capable of replacing backup software and hardware in some very large environments. Technologies such as data deduplication, thin provisioning and compression have increased the effective capacity of disk arrays, further enhancing the appeal of these turnkey systems. And because processing power and network connectivity is so affordable these days, it's possible to implement these features without significantly impacting the ingest and throughput speed of the appliance.

These developments have made backup appliances a better fit for IT departments in larger organizations, but there's another factor to consider. The simplicity that makes appliances attractive to smaller companies is also appealing to larger IT organizations. After all, time saved on more basic tasks like backup administration can be redirected to other, more complex projects.

Advantages and disadvantages of backup appliances

Generally, an appliance is easier to implement than an independent software application because the appliance comes with the backup software installed and configured on the server hardware -- the right server hardware. There are no platform compatibility issues and the configurations available are optimized for the software. As turnkey solutions, appliances include at least the initial storage hardware required to get up and running. Many allow users to add more disk capacity and tape, eliminating another potential variable in the process. In addition to implementation benefits, appliances can save on acquisition costs compared to buying separate hardware and software components, and provide operational savings by consolidating hardware and software support.

The characteristics that make appliances easy to implement can also make them somewhat inflexible and less scalable. The manufacturer can only provide a finite number of hardware choices, compared with the range of server and storage hardware that backup software alone can support. Although scalability of these appliances has improved, limitations remain that may result in capacity problems when data sets grow; limited software features can mean a lack of platform or application support. Also, buying the entire system from a single vendor may mean you'll have to pay more for capacity upgrades since you're locked in to that supplier. When the appliance has finally reached full capacity, you'll have to deal with a "forklift" upgrade to a larger unit or with managing two separate backup appliances.

Replace rather than reuse

As turnkey solutions, most data backup appliances don't allow you to incorporate existing assets, although some do support an existing backup software implementation. This could mean you end up buying hardware and software to replace similar assets you already have that may not be fully depreciated. So implementing a backup appliance may be a better solution if you're looking to replace something that's totally outgrown or you need to move up from a departmental or small business system.

Appliance sampler

All the backup appliances described here include dedupe, so it's not singled out as a feature for any of the products, although some very real differences do exist between the ways these products handle data reduction. Cloud connectivity and cloud backup features are not specifically addressed for the same reason. Those two aspects of a data backup appliance are discussed in the "Data backup appliance selection criteria" section of this article.

EVault Inc. Before being acquired by Seagate Technology LLC in 2006, EVault started as a cloud backup service that provided consumer and small business backup services. A few years later, the firm added a local storage appliance to its offering, making them more than just a storage-as-a-service backup offering. Its current lineup provides usable capacity of up to 24 TB per appliance with support for all major platforms and many apps. EVault appliance features include bare-metal restore to dissimilar hardware, replication with bandwidth throttling, and concurrent backup and restore/replication.

STORServer Inc. STORServer took what might be called a hybrid approach to its product development, marrying an existing backup application, IBM's Tivoli Storage Manager (TSM), with purpose-built hardware. While TSM is typically considered an "enterprise" backup application, STORServer has made its data backup appliances easy for even small companies to use.

TSM's architecture uses a relational database that abstracts the logical data from the physical storage, allowing STORServer to scale much larger than other architectures. This also gives them the flexibility to evolve the hardware and software independently, without disrupting the existing data set. In business for more than a dozen years, the company's backup appliances scale to hundreds of terabytes of disk capacity, with solid-state storage and tape options. Client support includes most Unix and Linux variants, as well as Windows and Mac OS. STORServer's application and database support are comprehensive and VMware integration is very thorough.

Symantec Corp. Symantec has been one of the primary backup software vendors for many years, going back to the days of Veritas and before that, OpenVision. The firm has now added appliances for its Backup Exec and NetBackup products by installing its software on industry-standard server hardware, creating a standalone backup solution that can be integrated into an existing Symantec environment as a media server. The NetBackup appliance provides up to 72 TB of capacity and the Backup Exec appliance provides up to 5.5 TB of usable capacity. As established backup software products, both support all major operating systems and applications, and offer a comprehensive list of advanced features.

Unitrends. Unitrends originally designed its backup appliances for small to midmarket companies with the intent of making backup simple and easy -- in their words, a "toaster mentality." The firm's line of appliances tops out at nearly 100 TB of usable capacity and its backup/recovery software (developed in-house) has a complete list of features, including advanced functionality such as (near) continuous data protection, VMware vStorage APIs for Data Protection vCenter integration, and support for "disk-to-disk-to-any" archiving for disaster recovery (DR) options and long-term retention.

Being in business for more than 20 years has enabled Unitrends to compile an extensive support matrix that includes 100-plus different versions of more than 40 operating systems in cloud, physical and virtual backup. This gives users a very comprehensive backup solution and allows them to migrate backup from old platforms easily.

Data backup appliance selection criteria

When evaluating a data backup appliance, or just deciding whether to replace a traditional backup infrastructure with one of these offerings, there are several things to think about. Aside from price and feature set, the following characteristics should also be considered.

Capacity and scalability. Whether it's scale-up, scale-out or a combination, some appliances expand better than others. Obviously, projected growth and long-term storage requirements should be contemplated.

In some cases, tape support may be appropriate because it provides the most capacity in the smallest footprint and the lowest cost for long-term storage.

Data reduction technologies can play a big part in the calculation of how much "effective capacity" a system has, so the data types most likely to populate the backup appliance should be known. You can then compare them with the compression, deduplication and thin provisioning technologies employed (see the section on data deduplication below).

Cloud plus backup appliance. Most backup appliances provide some form of cloud integration, whether it's the ability to send backups to the vendor's cloud for DR purposes or to a public cloud provider such as Amazon or Rackspace. Since backups (and restores) involve so much data, care must be taken to understand how much data the backup appliance will actually send "over the wire" and how well it optimizes WAN bandwidth to the cloud. Efficiently handling specific data objects created by software applications, also called "application intelligence," can greatly impact the cloud backup experience, so these details should be understood.

Data deduplication. Deduplication has evolved from an obscure technology that helped launch the disk backup product category, to an almost checkbox feature included in most backup hardware and software. However, there are many variations of the technology that operate very differently and produce a wide range of data reduction ratios, but all are called "deduplication."

The specific methods used for deduplication vary widely, such as:

The length of data segments being compared

Where in the ingest process comparisons take place

How the hash value for each segment is calculated

Where that hash table is stored

This makes it incumbent upon users evaluating a backup appliance to understand how its dedupe works, as well as how much data reduction it can produce on their specific data types in their specific backup environments.

The bottom line

The appliance format has become very popular for IT organizations because it simplifies the implementation of new infrastructure and often reduces operational expense. For many applications the cloud has offered an even simpler usage model and has replaced the use of hardware appliances.

However, backup touches most of the data in the environment on a regular basis, and can send terabytes of data to the backup storage device every day. This makes on-site infrastructure practically the only way to maintain reasonable performance, both for backups and restores, and to keep bandwidth costs under control.

Backup appliances can now provide most of the functionality that even larger companies need from their data protection systems. And, until companies have all their data running on applications in the cloud, a local data backup appliance will still be an attractive alternative.

About the author:Eric Slack is a senior analyst at Storage Switzerland.

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